1. Field of the Invention
The present invention relates to a method of producing a separated lipid/protein complex having a lipid content of 45% or more, i.e., a lipid-rich lipid/protein complex, and native proteins, from oil seeds and, more particularly, to a method of efficiently separating and producing lipid-rich lipid/protein complex and native proteins from oil seeds in a manner different from methods of producing lipids by conventional organic solvent extraction or enzymatic lipid extraction.
2. Discussion of the Background
In addition to the method of extraction with organic solvents such as hexane (the solvent extraction method) and the pressing method for producing lipids from oil seeds, a method (the enzymatic method) of extracting lipids by enzymatically macerating tissues of oil seeds has also been evaluated as an environmentally friendly method.
However, the solvent extraction method requires extraction facilities in order to use organic solvents as well as facilities for completely removing the solvent remaining in crude lipid and protein fractions after solvent extraction, and a large amount of initial investment is therefore required. Further, the loss of the solvent during the extraction operation is inevitable, and what is more, it is highly possible for the organic solvent to be released into the atmosphere. Recently, it has been reported that the released solvent lead to destruction of the ozone layer.
In the compressing method for the recovery of lipid from lipid-rich olive (Japanese Unexamined Patent Publication No. 5-59390) as a starting material, the enzymatic method has recently been proposed and put to practical use.
However, the lipids such as in olive, coconut oil etc. occurring in the middle pericarp are significantly different in the state of their presence from lipids occurring in oil seeds such as soybeans, rapeseeds, sunflower, sesame seeds, etc. That is, lipids such as in olives are present as free neutral lipids in its middle pericarp, while neutral lipids in the oil seeds are present in an organelle called an xe2x80x9coil bodyxe2x80x9d including fine particles of neutral lipids covered with phospholipids and a basic protein known as xe2x80x9coleosinxe2x80x9d.
Accordingly, if the enzymatic method is used, neutral lipids such as contained in the middle pericap of olives can be easily extracted. However, when lipids present as storage lipids in the organelle called xe2x80x9coil bodyxe2x80x9d are enzymatically extracted, the lipids easily form an emulsion with neutral lipids, phospholipids, basic protein and a lot of storage protein as well as with partially digested materials thereof, and the oil layer is very difficult to separate from the composition containing such an emulsion once formed. That is, fractions such as an oil layer, emulsion layer, aqueous layer and residue, each having slightly different specific gravity, are very difficult to separate by centrifugation from the composition consisting of the fractions.
In separating and producing storage proteins such as soybean storage proteins useful as food materials from oil seeds such as soybeans etc., it is generally necessary that soybean neutral lipids are first extracted by the organic solvent method and then the solvent present in the defatted soybeans is removed under reduced pressure or by heating.
xe2x80x9cSoybean protein isolatesxe2x80x9d are produced as food material by water-extraction of soybean protein from the resulting defatted soybeans and then drying its isoelectric precipitate. However, this protein has undergone denaturation with organic solvent and has been subjected to the heating and drying steps, and thus its partial denaturation is inevitable.
The object of the present invention is to efficiently and cheaply provide a lipid-rich lipid/protein complex having superior properties as a neutral lipid as well as native proteins derived from oil seeds using an environmentally friendly and industrially facile procedure to overcome the problem and drawbacks of other methods for separating and recovering neutral lipids and proteins from various oil seeds. The lipid-rich lipid/protein complex in the present invention refers to a lipid/protein complex, wherein the neutral lipid content is 45% or more and wherein the lipid/protein ratio by weight in lipid-rich lipid/protein complex is concentrated by 2.0 times or more as a relative ratio, based on the lipid/protein ratio in the oil seeds used as the raw material. Here, the lipid/protein absolute (weight) ratio in the raw material varies depending on the raw material (for example, about 0.5 in soybeans, about 1.8 in rapeseeds, and so on). The lipid/protein ratio in lipid-rich lipid/protein complex recovered is defined as a relative ratio, assuming that the absolute lipid/protein ratio in the raw material is defined to be 1.0.
To experimentally isolate and recovery the above-described xe2x80x9coil bodyxe2x80x9d present in oil seed cells, a method of utilizing an ultracentrifuge is used to take advantage of the slight difference in the specific gravity of each fraction. However, because industrial utilization of this apparatus is difficult, the present inventors examined the industrial method of easily separating and recovering the lipid rich-lipid/protein complex as well as the native proteins by aggregating the xe2x80x9coil bodyxe2x80x9d with a part of storage proteins in oil seeds and sedimenting or floating the resulting aggregates by low-speed centrifugation.
The object of the present invention is to provide a method of separating and producing lipid rich-lipid/protein complex containing considerable quantities of neutral lipids of superior quality and native proteins, from oil seeds.
Accordingly, the objects of the present invention, and others, may be accomplished with a method of separating and producing a lipid-rich lipid/protein complex and native proteins from oil seeds, by:
adding a substance having an ability to aggregate lipids with proteins to a water extract of oil seeds which contains lipids and proteins native to the oil seeds, to produce a sedimenting or floating lipid-rich lipid/protein complex, where the lipid content of the complex is at least 45% per aggregate;
isolating the complex; and
isolating the native proteins.
Thus, the present invention is a method of separating and recovering lipid rich-lipid/protein complex and native proteins from oil seeds, which comprises adding a substance having an ability to aggregate lipids with a part of proteins, sedimenting or floating the resulting lipid rich-lipid/protein complex as an aggregate including a lipid content of 45% or more and being concentrated by 2.0 or more by weight in terms of relative lipid/protein ratio based on that of the raw material, and recovering it for separation from native proteins.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description.